During the injection or extrusion molding of a crystalline thermoplastic polyalkylene arylate resin (e.g. as represented by polyalkylene terephthalate), the rate of crystallization of the resin when cooled has a great influence on the molding time (molding cycle time), and thus influences the productivity (economic efficiency) relating to making molded articles from such resin. Known methods for accelerating the crystallization rate by raising the crystallization temperature include adding an inorganic filler, such as boron nitride or talc, to the polyalkylene arylate resin. However, when a crystalline thermoplastic polyalkylene arylate resin containing such a filler is extruded into a film, small spots (called "fish eyes" in art parlance) will be present in the film presumably due to the nonuniform rate of crystallization that ensues. The resulting film is understandably of little commercial value. In order to solve this problem, the mixture comprised of crystalline thermoplastic polyalkylene arylate resin and inorganic filler must be further processed (i.e., the mixture must be subjected to high shearing force in an extruder for prolonged time periods) to thereby convert the mixture into a homogeneous dispersion. Such further processing, however, lowers the molecular weight of the resin in many cases yielding molded articles having poor physical characteristics.
The present invention is thus directed towards a solution to the above-described problems. More specifically, the present invention is based upon the discovery that, by adding a specific copolymer comprised of a specific alkylene arylate segment exhibiting smectic liquid crystallinity, and an ordinary polyalkylene arylate segment not exhibiting smectic liquid crystallinity, to a crystalline polyalkylene arylate base resin, significant improvements in the crystallization rate can be obtained. In addition, the problems associated with conventional techniques to improve crystallization rates (e.g. so-called "fish eyes" in formed films) are overcome.